Automatic focusing device

ABSTRACT

An apparatus for use with a camera or the like for determining the distance to a subject of interest. First and second lenses are provided. Modulated radiant energy of predetermined frequency is transmitted through the first lens toward the subject. The reflected image from the subject is passed by the second lens and received by a light sensitive transducer. The energy emitting source and the light sensitive transducer are displaced in unison to vary the modulated radiant energy received by the light sensitive transducer. Electronic detection circuitry is coupled to the light sensitive transducer to develop an output signal when the modulated radiant energy incident on the light sensitive transducer is at a maximum. The output signal is applied to arrest further displacement of the energy emitting source and the light sensitive transducer.

Unite tates Patent n 1 Harvey [45] Set. 11, was

[ AUTOMATIC FOCUSING DEVICE [75] inventor: Donald M. Harvey, Webster,NY.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

[22] Filed: Feb. 10, 1971 [21] Appl. No.: 114,335

Related US. Application Data [62] Division of Ser. No. 853,093, Aug. 26,1969, Pat. No.

[521 lJ.S. Cl 356/4, 250/201, 95/44 C [51] lnt. Cl Gtllc 3/08 [58] Fieldof Search 356/4; 250/201; 95/44 C [56] References Cited UNITED STATESPATENTS 3,435,744 4/1969 Stimson 3,274,9l3 9/1966 Biedermann et al 95/44C POWER SUPPLY BANDPASS VAL-Q58 l 60 Primary ExaminerBenjamin A.Borchelt Assistant Examiner-S. C. Buczinski Attorney-Robert W.l-lfiiptofiiwilliam H. .l. Kline et a1. i

[5 7 ABSTRACT An apparatus for use with a camera or the like fordetermining the distance to a subject of interest. First and secondlenses are provided. Modulated radiant energy of predetermined frequencyis transmitted through the first lens toward the subject. The reflectedimage from the subject is passed by the second lens and received by alight sensitive transducer. The energy emitting source and the lightsensitive transducer are displaced in unison to vary the modulatedradiant energy received by the light sensitive transducer. Electronicdetection circuitry is coupled to the light sensitive transducer todevelop an output signal when the modulated radiant energy incident onthe light sensitive transducer is at a maximum. The output signal isapplied to arrest further displacement of the energy emitting source andthe light sensitive transducer.

16 Claims, 7 Drawing Figures TRIGGER FILTER CIRCUT PAIENTEDSIP! 1 1 sum1 or 3 74 FIG. '6

AUTOMATIC FOCUSING DEVICE This is a division of US. Pat. aPplicationSer. No. 853,093, filed Aug. 26, 1969 now U.S. Pat. No. 3,599,552.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an automatic focusing and range finder mechanism suitable foruse in a camera or the like.

2. Description of the Prior Art It is broadly known in the prior art touse reflected light from a subject for the purpose of determining rangedistance. One of the major difficulties in the art has been toeffectively use the reflected signal so as to precisely determine whentrue focus occurs.

SUMMARY OF THE INVENTION The invention relates to an apparatus fordetermining the range distance to a subject of interest. In onedisclosed embodiment of the invention, energy emitting means areprovided for transmitting modulated radiant energy of predeterminedfrequency through a first lens towardthe subject. The reflected imagefrom the subject is received by a second Ines and passed to a lightsensitive means. Displacement means are adapted to move the energyemitting means and the light sensitive means in unison to vary themodulated radiant energy received by the light sensitive means. Meansare coupled to the light sensitive means for developing an output signalwhen the modulated radiant energy incident on the light sensitive meansis at a maximum.

In another embodiment, the first and second lenses are masked so as toexaggerate out of focus conditions to enable easier detection of themaximum modulated radiant energy incident on the light sensitive means.

It is an object of the instant invention to porvide an automaticmechanism which will quickly and accurately enable the determination ofdistance without elaborate manual manipulation being required.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawings.

'BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view of a stillcamera utilizing an automatic focus and range finding mechanism inaccordance with the invention;

FIG. 2 is a schematic diagram showing the automatic focus and rangefinding mechanism in accordance with one illustrative embodiment of theinstant invention;

FIG. 3 is a wave form diagram of photocurrent vs. lens displacement usedin explaining the operation of the embodiment of FIG. 2;

FIG. 4 is a schematic diagram showing a second illustrative embodimentof the instant invention;

FIG. 5 is a wave form diagram of photocurrent vs. lens displacement usedin explaining the operation of the embodiment of FIG. 4; and

FIGS. 6 and 7 are explanatory schematic diagrams of certain componentsfound in the embodiment of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is hereillustrated in conjunction with a still camera, but it should of coursebe understood that the inventive concept is equally useful in anyapparatus where automatic focus and range finding are required to beaccomplished.

Referring now to FIG. 11, a still camera is indicated generally at it).The camera Ml) includes: an objective lens indicated at 12, a shuttersetting dial M, a photometric detector il6, a view finder llfi, a rangeand focus mechanism release member 20, a shutter release member 22, anda winding advance member 24. In accordance with the invention, thecamera also includes a focus and range determining mechanism indicatedgenerally at 26 in FIG. 1; lenses 23, 36 shown in FIG. l are associatedwith this mechanism and shall later be described in greater detail.

One embodiment of the automatic focus and range determining mechanism ofthe instant invention is illustrated inFlG. 2. A source of modulatedradiation is indicated generally at 32, and in this particularembodiment may conveniently comprise an incandescent lamp 34 having astraight line filament 356. The radiant energy emitted by the lamp 34 ismodulated in any convenient manner such as by a mechanical chopperindicated at 38 and suitably driven by a prime mover source (not shown)to provide a predetermined modulated frequency.

A photosensitive transducer means, indicated generally at 40, comprisesa photosensitive cell surface 42. While the radiation source 32 and thetransducer 40 may be conveniently arranged in a housing 44, they mayalso be independently supported. As will be seen as the descriptionproceeds, the radiation source 32 and the photosensitive transducermeans 40 are moved in unison. An electric motor 46 is mechanicallycoupled to the housing 44, as indicated symbolically at d7, so as tomove the modulated radiation source 32 and the photosensitive transducermeans W in the direction indicated by the arrow at 4%. The motor 46 isenergized by power supply 49, when the release member 2% is actuated toclose switch 53, and is arranged to be displaced through a predeterminedrotational displacement based on the total distance housing 44 is to bemoved, i.e., from the near hyperfocal setting for the objective lens 12of the camera. The motor 46 is biased by spring means 51 to return toits initial position after the motor shaft is unclamped, as will beexplained when the operation of the FIG. 2 embodiment is discussed ingreater detail. A range determining cam means 50, having a cam surfacewhich is a function of range distance, is coupled, as indicated by thedashed line, for rotational displacement with the motor shaft. Theobjective lens .12 in this embodiment is coupled directly to the cammeans 50 by means (not shown) which include a follower to engage thecontoured surface of cam means 50. As the cam 50 rotates, the objectivelens 112 is successively moved through various focal settings untildisplacement is arrested at true focus for the subject.

The lightfrom the straight line filament 36, after modulation by thechopper 38, is projected toward a subject, indicated here symbolicallyby a planar surface identified at 66, to producean image at 52 which isreflected to and received by the lens 30 and imaged on the photocellsurface 42.

The electrical output of the photosensitive transducer means 40 iselectrically coupled to a band pass filter means 54, and thensuccessively passed to an amplifier means 56, a peak detector means 58,and a trigger circuit means 60. The output signal of the trigger circuit66 is applied to a clamping means 62.

Completing the description of FIG. 2, the shutter release member 22 isadapted to open switch 53, and is coupled to a shutter indicatedsymbolically at S, as will be later explained.

OPERATION OF THE PREFERRED EMBODIMENT In operation of the camera, theoperator observes a subject 66 through the view finder I8 (FIG. I), andthe focus determining release member 26 is depressed to close switch 53to energize the electric motor 66 and the circuitry at 54, 56, 56, 60and 62. Switch 53 is arranged to remain closed after release of member20 and to be subsequently opened by operation of the shutter releasemember 22. The rotation of the motor 46 causes the housing 44 to bedisplaced in the direction indicated by the arrow 48.

Referring now especially to FIG. 2, when the filament is in true focuson the subject 66, the line filament will be imaged at 52. In any otherposition either side of true focus, the filament imaged on the subject66 will be enlarged as indicated in dotted outline at 68. The enlargedimage will therefore be reflected as an enlarged image on the photocellsurface 42 as indicated at 70.

In FIG. 3 there is a curve depicting photocurrent as ordinate and lensdisplacement as abscissa. When the line filament 36 is in true focus onthe subject 66, maximum photocurrent will obtain as indicated by theordinate at 64. In any other position a smaller photocurrent willresult. When, for example, the photocell receives the image indicated at70, a smaller photocurrent will be obtained because the photosensitivesurface is receiving less radiant energy.

The light transmitted from the source of radiation 32 is modulated bythe mechanical chopper 36; the signal reflected to the photocell surface62 is thus also modulated. The band pass filter S4 is arranged to pass aband of frequencies including the predetermined frequency such as forexample, 2.5 kilo Hz. The modulated photocurrent fro photosensitivetransducer means 40 is passed to the band pass filter 54, whichattenuates other frequencies outside the band. The filtered output ispassed to amplifier 56 and then to a peak detector 58 which, when themaximum signal is detected, sends an output to the trigger circuit means60 which sends a trigger signal to the clamping means 62, which mayinclude solenoids energized in response to said trigger signal to holdthe motor shaft against further rotation. The range determining cam 50,which is mounted on the motor shaft, then comes to rest, and since theobjective lens i2 is in continguous contact with the cam 50, theobjective lens 12 is now in correct focus with respect to the subject66. I

The objective lens 12 of the camera 10 is now in focus, and the camerauser depresses the shutter release member 22, which first permits lightto enter the camera through the objective lens 12 for actual picturetaking, and then opens switch 53 to disconnect the power supply 49 tothereby deenergize the circuitry 54, 56, 56!, 60, 62 as well as themotor 46. Next, the spring means 51 rotates motor 46 to return thehousing 44 to its initial position.

DESCRIPTION OF AN ALTERNATIVE EMBODIMENT detection. The embodiment ofFIG. 4 is intended to provide a photocurrent vs. lens displacement curvesimilar to that depicted in FIG. 5, where, with the same radiationsource 32, a somewhat sharper peak obtains, although with some sacrificein the signal amplitude. As will be understood presently, it ispreferable to sacrifice the diminution in signal magnitude in order toprovide for easier peak detection. (If one desires that there be no lossof signal amplitude, then one need only increase the magnitude of theradiation source 32.)

Referring especially now to FIG. 4, where the same numeration has beenretained in identifying similar parts, the lens 28 is partially coveredby masking members 72, 74, and the lens 30 contains a masking element 76positionedon its optical axis.

This arrangement of the lenses 28, 30 may best be appreciated from astudy of FIGS. 6 and 7. The use of the masking means 72, 74 (FIG. 6)narrows the width of the light beam being sent out from the source ofradiation 32 toward the subject 66. As shown in FIG. 7, the reflectedenergy from the subject 66 is then passed through the lens 30, which,because of the mask 76, refracts the received light in a pattern havingthe general configuration of a centrally hollowed cone, as indicated bycross section at 78, 80.

In both the FIG. 2 and FIG. 4 embodiments the lens 12 may be eitherdisplaced concurrently with the cam 56 or the lens may be later movedtoward the stop afforded by the arrested cam 50 prior to picture taking.

In the FIG. 4 embodiment, the lens 112 is not displaced concurrentlywith the cam 50; instead, objective lens 12 is arranged to be displacedtoward the cam surface of cam 50 upon actuation by the shutter releasemember 22. This may be accomplished in one convenient manner by biasingthe lens.12 in the direction of the cam surface of cam 50, the lens 12being held out of contact with the cam surface by any suitable latchingmeans. Depressing shutter member 22, then, releases OPERATION OF THEALTERNATIVE EMBODIMENT The operation of the device is substantially thesame as previously described in connection with FIG. 2. As

before, the camera user depresses the range and focus determining member20 to energize the motor 46 and the circuitry; the housing 46 supportingthe radiation source-photosensitive transducer 32-40 is then dis placedin the direction 48. The modulated light received by the lens 30 ispassed to the photosensitive transducer 40 in the form of a centrallyhollowed cone, as indicated by the cross hatching 78, 80 in FIG. 7. Themaximum light falls on the photocell surface 4'52 when the filamentimage 36 is in true focus. At any point on either side of true focus,the refracted light pattern of the centrally hollowed cone eicaggeratesthe out of focus condition so that substantially less light falls on thephotocell surface 42, resulting in the sharper peak depicted in lFlG. d.

lPeal detection is accomplished as described in connection with theembodiment of H6. 2, and when the true range has been determined, thecamera user depresses the shutter member 22, which first: (a) causesobjective lens 112 to be displaced toward the stop afforded by thearrested cam fill, then (b) actuates the shutter S, and finally (c) openswitch $31 to tie-energize the motor as and the circuitry. The motor asunder the discipline of the spring means till returns to the restposition, as does the housing Ml.

As viewed in the direction indicated by the arrow $2 (FIGS. 2 and d), onthe frontal plane orthographic projection the height dimensions of thewire filament 356 and the photoemissive surface of the photosensitivetransducer means are defined as hll and k2 respectively. (The diameterdimension of the wire filament 3b is equal to hi.) The lenses 2% andFill have focal lengths fl and f2 respectively. The focal lengths fl andf2 and the heights hll and h2 are in inverse proportion. Statedmathematically:

it should be noted that the above equation holds true for equal focallengths fl and f2, since this produces a ratio equal to unity.

The invention has been described in detail with particular reference tothe illustrated embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof theinvention.

l claim:

ll. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens;

b. a second lens;

c. means for emitting radiant energy of predetermined frequency throughsaid first lens toward the subject;

d. light sensitive means for receiving through said second lens emittedradiant energy reflected from the subject;

e. means for translating along parallel axes said energy emitting meansand said light sensitive means in unison with respect to the subject tovary the emitted radiant energy received by said light sensitive means;and

f. means coupled to said light sensitive means for developing an outputsignal when the emitted radiant energy received by said light sensitivemeans is at a maximum.

2. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens having a first focal length;

b. a second lens having a second focal length;

c. means comprising a radiation surface having an effective height h] infrontal plane orthographic orientation for emitting modulated radiantenergy through said first lens toward the subject;

d. light sensitive means comprising a light sensitive surface having aheight k2 in said frontal plane orthographic orientation, said heightshi and k2 being in inverse proportion to said first and second focallengths, said light sensitive means receiving through said second lensmodulated radiant energy reflected from the subject;

e. means for displacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means; and

f. means coupled to said light sensitive means for developing an outputsignal when the modulated radiant energy received by said lightsensitive means is at a maximum.

3. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens;

b. a second lens;

0. means for emitting modulated radiant energy of predeterminedfrequency through said first lens toward the subject;

(1. light sensitive means for receiving through said second lensmodulated radiant energy reflected from the subject;

e. means for translating along parallel axes said energy emitting meansand said light sensitive means in unison with respect to the subject tovary the modulated radiant energy received by said light sensitivemeans;

it. electronic detection means coupled to said light sensitive means fordeveloping an output signal when the radiant energy received by saidlight sensitive means is at a maximum; and

g. utilization means for utilizing said output signal to arrest saidtranslation of said energy emitting means and said light sensitivemeans.

4. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens having a first focal length;

b. a second lens having a second focal length;

c. means comprising a radiation surface having an effective height hllin frontal plane orthographic orientation for emitting modulated radiantenergy through said first lens toward the subject;

d. light sensitive means comprising a light sensitive surface having aheight 112 in said frontal plane orthographic orientation, said heightshi and k2 being in inverse proportion to said first and second focallengths, said light sensitive means receiving through said second lensmodulated radiant energy reflected from the subject; I

e. means for displacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means;

f. electronic detection means coupled to said light sensitive means fordeveloping an output signal when the modulated radiant energy receivedby said light sensitive means is at a maximum; and

g. utilization means for utilizing said output signal to arrestdisplacement of said energy emitting means and'said light sensitivemeans.

5. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens;

b. first means for mashing said first lens to provide a transmissionpath;

c. a second lens;

d. second means for masking said second lens to provide a transmissionpath;

e. means for emitting modulated radiant energy of predeterminedfrequency through said first lens toward the subject;

f. light sensitive means for receiving through said second lensmodulated radiant energy reflected from the subject;

g. means for dsiplacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means; and

h. means coupled to said light sensitive means for developing an outputsignal when the modulated radiant energy received by said lightsensitive means is at a maximum.

6. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens having a first focal length;

b. first means for masking said first lens to provide a transmissionpath;

c. a second lens having a second focal length;

d. second means for masking said second lens to provide a transmissionpath;

e. means comprising a radiation surface having an effective height hl infrontal plane orthographic orientation for emitting modulated radiantenergy through said first lens toward the subject;

f. light sensitive means comprising a light sensitive surface having aheight h2 in said frontal plane orthographic orientation, said heightshi and k2 being in inverse proportion to said first and second focallengths, said light sensitive means receiving through said second lensmodulated radiant energy reflected from the subject;

g. means for displacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means; and

h. means coupled to said light sensitive means for developing an outputsignal when the modulated radiant energy received by said lightsensitive means is at a maximum.

7. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens;

b. first means for masking said first lens to provide a transmissionpath;

0. a second lens;

d. second means for masking said second lens to provide a transmissionpath;

e. means for emitting modulated radiant energy of predeterminedfrequency through said first lens toward the subject;

f. light sensitive means for receiving through said sec ond lensmodulated radiant energy reflected from the subject;

g. means for displacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means;

h. electronic detection means coupled to said light sensitive means fordeveloping an output signal when the modulated radiant energy receivedby said light sensitive means is at a maximum; and

. utilization means for utilizing said output signal to arrestdisplacement of said energy emitting means and said light sensitivemeans.

8. Apparatus for determining the distance to a subject of interestcomprising:

a. a first lens having a first focal length;

b. first means for masking said first lens to provide a transmissionpath;

0. a second lens having a second focal length;

(1. second means for masking said second lens to provide a transmissionpath;

e. source means comprising a radiation surface having an effectiveheight hl in frontal plane orthographic orientation for emittingmodulated radiant energy through said first lens toward the subject;

f. light sensitive means comprising a light sensitive surface having aheight h2 in said frontal plane orthographic orientation, said heightshi and k2 being in inverse proportion to said first and second focallengths, said light sensitive means receiving through said second lensmodulated radiant energy reflected from the subject;

g. means for displacing said energy emitting means and said lightsensitive means in unison to vary the modulated radiant energy receivedby said light sensitive means;

h. electronic detection means coupled to said light sensitive means fordeveloping an output signal when the radiant energy received by saidlight sensitive means is at a maximum; and

i. utilization means for utilizing said output signal to arrestdisplacement of said energy emitting means and said light sensitivemeans.

9. Apparatus according to claim 1 wherein:

c. said energy emitting means is an incandescent lamp comprising astraight line filament; and

d. said light sensitive means is a photocell.

10. Apparatus according to claim 2 wherein:

c. said energy emitting means is an incandescent lamp comprising astraight line filament wound in the form of a helix having a diameterequal to said height hi; and

d. said light sensitive means comprises a photocell having an exposedlight sensitive surface having a height equal to said height 112.

11. Apparatus according to claim 5 wherein:

e. said energy emitting means is an incandescent lamp comprising astraight line filament; and

f. said light sensitive means is a photocell.

12. Apparatus according to claim 6 wherein:

e. said energy emitting means is an incandescent lamp comprising astraight line filament wound in the form of a helix having a diameterequal to the height hi; and

f. said light sensitive means comprises a photocell having an exposedlight sensitive surface having a height equal to said height 112.

' 13. Apparatus according to claim 1 wherein said means coupled to saidlight sensitive means comprises band pass filter means, amplifier means,peak detector means, and output circuit means connected in cascade, saidoutput circuit means delivering said output signal.

14. Apparatus according to claim 2 wherein said means coupled to saidlight sensitive means comprises band pass filter means, amplifier means,peak detector means, and output circuit means connected in cascade, saidoutput circuit means delivering said output signal. 15. Apparatusaccording to claim 4 wherein said electronic detection means comprisesband pass filter means, amplifier means, peak detector means, and outputcircuit means connected in cascade, said band pass filter means beingcoupled to said light sensitive means, said output circuit meansproducing said output signal.

to. Apparatus according to claim 6 wherein said means, and outputcircuit means connected in cascade, said band pass filter means beingcoupled to said light sensitive means, said output circuit meansproducing means coupled to said light sensitive means comprises Said p"Signalband pass filter means, amplifier means, peak detector

1. Apparatus for determining the distance to a subject of interestcomprising: a. a first lens; b. a second lens; c. means for emittingradiant energy of predetermined frequency through said first lens towardthe subject; d. light sensitive means for receiving through said secondlens emitted radiant energy reflected from the subject; e. means fortranslating along parallel axes said energy emitting means and saidlight sensitive means in unison with respect to the subject to vary theemitted radiant energy received by said light sensitive means; and f.means coupled to said light sensitive means for developing an outputsignal when the emitted radiant energy received by said light sensitivemeans is at a maximum.
 2. Apparatus for determining the distance to asubject of interest comprising: a. a first lens having a first focallength; b. a second lens having a second focal length; c. meanscomprising a radiation surface having an effective height h1 in frontalplane orthographic orientation for emitting modulated radiant energythrough said first lens toward the subject; d. light sensitive meanscomprising a light sensitive surface having a height h2 in said frontalplane orthographic orientation, said heights h1 and h2 being in inverseproportion to said first and second focal lengths, said light sensitivemeans receiving through said second lens modulated radiant energyreflected from the subject; e. means for displacing said energy emittingmeans and said light sensitive means in unison to vary the modulatedradiant energy received by said light sensitive means; and f. meanscoupled to said light sensitive means for developing an output signalwhen the modulated radiant energy received by said light sensitive meansis at a maximum.
 3. Apparatus for determining the distance to a subjectof interest comprising: a. a first lens; b. a second lens; c. means foremitting modulated radiant energy of predetermined frequency throughsaid first lens toward the subject; d. light sensitive means forreceiving through said second lens modulated radiant energy reflectedfrom the subject; e. means for translating along parallel axes saidenergy emitting means and said light sensitive means in unison withrespect to the subject to vary the modulated radiant energy received bysaid light sensitive means; f. electronic detection means coupled tosaid light sensitive means for developing an output signal when theradiant energy received by said light sensitive means is at a maximum;and g. utilization means for utilizing said output signal to arrest saidtranslation of said energy emitting means and said light sensitivemeans.
 4. Apparatus for determining the distance to a subject ofinterest comprising: a. a first lens having a first focal length; b. asecond lens having a second focal length; c. means comprising aradiation surface having an effective height h1 in frontal planeorthographic orientation for emitting modulated radiant energy throughsaid first lens toward the subject; d. light sensitive means comprisinga light sensitive surface having a height h2 in said frontal planeorthographic orientation, said heights h1 and h2 being in inverseproportion to said first and second focal lengths, said light sensitivemeans receiving through said second lens modulated radiant energyreflected from the subject; e. means for displacing said energy emittingmeans and said light sensitive means in unison to vary the modulatedradiant energy received by said light sensitive means; f. electronicdetection means coupled to said light sensitive means for developing anoutput signal when the modulated radiant energy received by said lightsensitive means is at a maximum; and g. utilization means for utilizingsaid output signal to arrest displacement of said energy emitting meansand said light Sensitive means.
 5. Apparatus for determining thedistance to a subject of interest comprising: a. a first lens; b. firstmeans for masking said first lens to provide a transmission path; c. asecond lens; d. second means for masking said second lens to provide atransmission path; e. means for emitting modulated radiant energy ofpredetermined frequency through said first lens toward the subject; f.light sensitive means for receiving through said second lens modulatedradiant energy reflected from the subject; g. means for dsiplacing saidenergy emitting means and said light sensitive means in unison to varythe modulated radiant energy received by said light sensitive means; andh. means coupled to said light sensitive means for developing an outputsignal when the modulated radiant energy received by said lightsensitive means is at a maximum.
 6. Apparatus for determining thedistance to a subject of interest comprising: a. a first lens having afirst focal length; b. first means for masking said first lens toprovide a transmission path; c. a second lens having a second focallength; d. second means for masking said second lens to provide atransmission path; e. means comprising a radiation surface having aneffective height h1 in frontal plane orthographic orientation foremitting modulated radiant energy through said first lens toward thesubject; f. light sensitive means comprising a light sensitive surfacehaving a height h2 in said frontal plane orthographic orientation, saidheights h1 and h2 being in inverse proportion to said first and secondfocal lengths, said light sensitive means receiving through said secondlens modulated radiant energy reflected from the subject; g. means fordisplacing said energy emitting means and said light sensitive means inunison to vary the modulated radiant energy received by said lightsensitive means; and h. means coupled to said light sensitive means fordeveloping an output signal when the modulated radiant energy receivedby said light sensitive means is at a maximum.
 7. Apparatus fordetermining the distance to a subject of interest comprising: a. a firstlens; b. first means for masking said first lens to provide atransmission path; c. a second lens; d. second means for masking saidsecond lens to provide a transmission path; e. means for emittingmodulated radiant energy of predetermined frequency through said firstlens toward the subject; f. light sensitive means for receiving throughsaid second lens modulated radiant energy reflected from the subject; g.means for displacing said energy emitting means and said light sensitivemeans in unison to vary the modulated radiant energy received by saidlight sensitive means; h. electronic detection means coupled to saidlight sensitive means for developing an output signal when the modulatedradiant energy received by said light sensitive means is at a maximum;and i. utilization means for utilizing said output signal to arrestdisplacement of said energy emitting means and said light sensitivemeans.
 8. Apparatus for determining the distance to a subject ofinterest comprising: a. a first lens having a first focal length; b.first means for masking said first lens to provide a transmission path;c. a second lens having a second focal length; d. second means formasking said second lens to provide a transmission path; e. source meanscomprising a radiation surface having an effective height h1 in frontalplane orthographic orientation for emitting modulated radiant energythrough said first lens toward the subject; f. light sensitive meanscomprising a light sensitive surface having a height h2 in said frontalplane orthographic orientation, said heights h1 and h2 being in inverseproportion to said first and second focal lengths, said light sensitivemeans receiving through Said second lens modulated radiant energyreflected from the subject; g. means for displacing said energy emittingmeans and said light sensitive means in unison to vary the modulatedradiant energy received by said light sensitive means; h. electronicdetection means coupled to said light sensitive means for developing anoutput signal when the radiant energy received by said light sensitivemeans is at a maximum; and i. utilization means for utilizing saidoutput signal to arrest displacement of said energy emitting means andsaid light sensitive means.
 9. Apparatus according to claim 1 wherein:c.'' said energy emitting means is an incandescent lamp comprising astraight line filament; and d.'' said light sensitive means is aphotocell.
 10. Apparatus according to claim 2 wherein: c.'' said energyemitting means is an incandescent lamp comprising a straight linefilament wound in the form of a helix having a diameter equal to saidheight h1; and d.'' said light sensitive means comprises a photocellhaving an exposed light sensitive surface having a height equal to saidheight h2.
 11. Apparatus according to claim 5 wherein: e.'' said energyemitting means is an incandescent lamp comprising a straight linefilament; and f.'' said light sensitive means is a photocell. 12.Apparatus according to claim 6 wherein: e.'' said energy emitting meansis an incandescent lamp comprising a straight line filament wound in theform of a helix having a diameter equal to the height h1; and f.'' saidlight sensitive means comprises a photocell having an exposed lightsensitive surface having a height equal to said height h2.
 13. Apparatusaccording to claim 1 wherein said means coupled to said light sensitivemeans comprises band pass filter means, amplifier means, peak detectormeans, and output circuit means connected in cascade, said outputcircuit means delivering said output signal.
 14. Apparatus according toclaim 2 wherein said means coupled to said light sensitive meanscomprises band pass filter means, amplifier means, peak detector means,and output circuit means connected in cascade, said output circuit meansdelivering said output signal.
 15. Apparatus according to claim 4wherein said electronic detection means comprises band pass filtermeans, amplifier means, peak detector means, and output circuit meansconnected in cascade, said band pass filter means being coupled to saidlight sensitive means, said output circuit means producing said outputsignal.
 16. Apparatus according to claim 6 wherein said means coupled tosaid light sensitive means comprises band pass filter means, amplifiermeans, peak detector means, and output circuit means connected incascade, said band pass filter means being coupled to said lightsensitive means, said output circuit means producing said output signal.